PROJECT SUMMARY Excess weight is a public health priority for all sectors of the US population and particularly for Black adolescents who have a disproportionately high prevalence of obesity and overweight. Research suggests that consumption of fast food and calorie dense foods prepared outside of the home contribute to a higher body mass index. Black youth are more likely than their White peers to live in low-income communities with a high density of fast food restaurants. There is a need for interventions to help adolescents make healthy choices in these obesogenic environments. Our clinical work in the Michigan Pediatric Outpatient Weight Evaluation and Reduction (MPOWER) program suggests that adolescents find it difficult to make healthy choices in obesogenic settings, such as fast food restaurants. From our initial MPOWERed Messages study, we found that adolescents welcomed health- related text messages (based on Self Determination Theory and Motivational Interviewing) if they viewed them as personally relevant and if they were received at times when they faced dietary choices. Based on these findings, we hypothesized that delivering messages (tailored to users? preferences and values) at a time and place when they are making a dietary choice (e.g., in a restaurant) would positively influence their selection. In a first step toward exploring this, we combined our experience in the development of tailored texts for adolescents, with state-of-the-art geo-fencing technology, to develop the Location Initiated Individualized Texts for African American Adolescent Health (LIITA3H) mobile application. This app a) accurately identified when users were in an eating venue such as a restaurant, b) automatically sent culturally relevant messages (based on focus group input from the target population) tailored to user preferences and the menu options at their location with the aim of prompting users to make a healthy choice, and c) allowed users to submit an annotated photo of their food choice. This study demonstrated the app?s acceptability and feasibility, and the accuracy of the technology to deliver tailored messages at the point of purchase. However, we did not pilot test whether receipt of these ?just in time? personalized messages, actually influenced participants? food choices. This R21 project will focus on 1) enhancing the LIITA3H app by incorporating user input regarding its design and by allowing greater automation in the identification of eating venues, and 2) pilot testing the impact of the app on the number of calories purchased from, and number of visits to, fast food restaurants. This will provide data regarding effect size, and will form the foundation for planning a future randomized trial which would include a larger population and a greater range of eating venues. A better understanding of how receipt of ?just in time? tailored messages, made possible by new location-based technology, alters behavior among a high risk population, will help future efforts to address obesity and other illnesses impacted by lifestyle choices.